SuperFGD prototype time resolution studies

THE charge-coupled device (CCD) has become the detector of choice in optical astronomy. CCDs provide a very linear response to detected photons, are very efficient at some wavelengths, and can now provide coverage of a relatively wide field of view1–3. But they become quite inefficient with decreasing wavelength, and they lack intrinsic wavelength and time resolution. The only way to select specific wavelengths is to place filters in front of the detector, which makes the total system less efficient. Time resolution can be achieved only with short exposures, which are possible only with very bright sources. Here we report a superconducting device that can overcome these limitations, and which has performance characteristics far superior to existing photon counting systems4–7. Our superconducting tunnel junction can detect individual photons at rates up to 2.5 kHz in the wavelength range 200–500 nm, with an intrinsic spectral resolution of 45 nm and a quantum efficiency estimated to be about 50 per cent. The theoretical resolution of the present device is ∼ 20 nm, but use of superconductors with lower transition temperature could improve that to 8 nm.

In order to improve the charged particle identification capability, end-cap time-of-flight (ETOF) detector of the Beijing Spectrometer (BESIII) has been upgraded with multi-gap resistive plate chamber (MRPC) technology, aiming at an overall time resolution of 80 ps for minimum-ionization particles to extend the K/ $$\pi $$ separation (2 $$\sigma $$ ) momentum range to 1.4 GeV/c. The previous version of ETOF in BESIII consisted of plastic scintillators. The multi-hit events distort both shape and amplitude of the output signals. MRPC technique was chosen for the BESIII ETOF upgrade as it provides high time resolution and high detection efficiency, is of relatively low cost and is insensitive to neutral particles. Most importantly, the fine segmentation of the MRPC readout stripes can suppress multi-hit events effectively. The final design of MRPC module for ETOF is characterized by double-stack (2 $$\times $$ 6) structure, dual-end readout mode and precision electronics. To batch-produce and test these MRPC modules, a series of tools and production procedures as well as related performance simulation and test methods were developed. Results showed that each MRPC module’s intrinsic time resolution (including the electronics contribution) is around 50 ps and the efficiency is better than 97%. The overall performance of the upgraded ETOF is better than the designed index. The new ETOF has been successfully installed at BESIII and run in 2016.

The FFIS spectrometer for determination of fission fragment mass distribution with the energy–velocity method

Chapter 76 - Transient two-dimensional infrared spectroscopy-towards measuring ultrafast structural dynamics

Low-level radioactive surface-contamination measurements require lightweight, large-area, and high-efficiency detectors. In the previous work, we utilized wavelength shifting (WLS) fibers, coupled to a beta-sensitive plastic scintillator (PS) layer on one side, and to an alpha-sensitive ZnS(Ag) layer on both sides, for detecting both alpha and beta particles. In this work, the main goal was to improve the light collection (maximizing the number of photons reaching the PMT) by optimizing the WLS fibers structure, for getting better signal-to-noise ratio and to minimize the low-energy threshold of the detector. In most cases, improving the light collection mostly influenced the detector resolution. In our case, improving the light collection will improve the detection efficiency by ability to detect more events at low-energy spectrum, which is limited by the noise level. Aiming to improve the scintillation light-collection efficiency, we investigated and compared four different detector configurations. Two of them described in the previous work presents utilization of WLS fibers, with different diameters ( $1~\hbox{mm}\phi $ , $1.5~\hbox{mm}\phi $ ), coupled on the PS. Two other configurations present utilization of WLS fibers ( $1.5~\hbox{mm}\phi $ ) installed into a flat groove on the PS layer, while in one configuration we utilized straight WLS fibers and in the other we utilized bent WLS fibers. It was found that the utilization of WLS fibers in bent configuration gives the highest light-collection efficiency. Additionally, there is improved light collection achieved by using WLS fibers with wider diameter ( $1.5~\hbox{mm}\phi $ ), which maximizes the capture fraction. Additionally, since ZnS(Ag) and PS have different decay times (200 ns and 2.4 ns, respectively), we were able to separate alpha from beta events. An algorithm script was developed to calculate the full width at half maximum (FWHM) of each pulse and a histogram was generated of the FWHM values for the pulse shape discrimination (PSD). Efficient PSD was achieved for alpha energies above 100 keV with figure of merit (FOM) of 1.92. GEANT4 simulation was carried out and compared with experimental results. The results of both were matched, showed that the light-collection efficiency from the bent WLS fibers configuration was the best. The simulation results and the experiments, including full description of the detector structure, ionization stage, and the WLS light collection, are presented.

A novel geometry for a sampling calorimeter employing inorganic scintillators as an active medium is presented. To overcome the mechanical challenges of construction, an innovative light collection geometry has been pioneered, that minimises the complexity of construction. First test results are presented, demonstrating a successful signal extraction. The geometry consists of a sampling calorimeter with passive absorber layers interleaved with layers of an active medium made of inorganic scintillating crystals. Wavelength-shifting (WLS) fibres run along the four long, chamfered edges of the stack, transporting the light to photodetectors at the rear. To maximise the amount of scintillation light reaching the WLS fibres, the scintillator chamfers are depolished. It is shown herein that this concept is working for cerium fluoride (CeF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) as a scintillator. Coupled to it, several different types of materials have been tested as WLS medium. In particular, materials that might be sufficiently resistant to the High-Luminosity Large Hadron Collider radiation environment, such as cerium-doped Lutetium-Yttrium Orthosilicate (LYSO) and cerium-doped quartz, are compared to conventional plastic WLS fibres. Finally, an outlook is presented on the possible optimisation of the different components, and the construction and commissioning of a full calorimeter cell prototype is presented.

Selecting and designing the front-end amplifier for high-gain photomultiplier detectors with optimal timing performance

We are currently developing a small animal positron emission tomography (PET) scanner with a design goal of 1 microlitre (1 mm3) image resolution. The detectors consist of a 12 × 12 array of 1 × 1 × 10 mm lutetium oxyorthosilicate (LSO) scintillator crystals coupled to a 64-channel photomultiplier tube (PMT) via 5 cm long optical fibre bundles. The optical fibre connection allows a high detector packing fraction despite the dead space surrounding the active region of the PMT. Optical fibre bundles made from different types of glass were tested for light transmission, and also their effects on crystal identification and energy resolution, and compared to direct coupling of the LSO arrays to the PMTs. We also investigated the effects of extramural absorber (EMA) in the fibre bundles. Based on these results, fibre bundles manufactured from F2 glass were selected. We built three pairs of prototype detectors (directly coupled LSO array, fibre bundle without EMA and fibre bundle with EMA) and measured flood histograms, energy resolution, intrinsic spatial resolution and timing resolution. The results demonstrated an intrinsic spatial resolution (FWHM) of 1.12 mm (directly coupled), 1.23 mm (fibre bundle without EMA coupling) and 1.27 mm (fibre bundle with EMA coupling) using an approximately 500 μm diameter Na-22 point source. Using a 330 μm outer diameter steel needle line source filled with F-18, spatial resolution for the detector with the EMA optical fibre bundle improved to 1.05 mm. The respective timing and energy FWHM values were 1.96 ns, 21% (directly coupled), 2.20 ns, 23% (fibre bundle without EMA) and 2.99 ns, 30% (fibre bundle with EMA). The peak-to-valley ratio in the flood histograms was better with EMA (5:1) compared to the optical fibre bundle without EMA (2.5:1), due to the decreased optical cross-talk. In comparison to the detectors used in our current generation microPET scanner, these detectors substantially improve on the spatial resolution, preserve the timing resolution and provide adequate energy resolution for a modern high-resolution animal PET tomograph.

Poor image quality limits clinical utility of dual-head gamma cameras for coincidence imaging. The use of thick crystals imposes one limitation. Conventional camera design results in parallax error due to an inability to measure depth-of-interaction (DOI). We are developing a modified gamma camera that measures DOI. The Depth-encoding Anger Detector incorporates a wavelength-shifting (WLS) optical fiber ribbon onto the face of an otherwise-conventional thick-crystal camera design. The conventional components compute x-y interaction coordinates and total energy signal. The WLS fiber ribbon measures DOI. We previously reported on the theoretical basis of the Depth-encoding Anger Detector and a prototype design. The diameter of a critical cone, defined by the indices of refraction of the NaI(Tl) and the WLS fibers, determines DOI. Scintillations within the cone propagate from the NaI(Tl) into the fibers; photons outside of the cone reflect back into the crystal. The Depth-encoding Anger Detector measures the cone's diameter to determine DOI. In this work, we report on simulation and experimental results from the Depth-encoding Anger Detector project. This includes the results of Detect2000 simulations used to examine different detector designs and the results of experimental measurements with the prototype system. While the simulations indicate feasibility of the concept, the simulations and experiments demonstrate that proper design and manufacture of the system are crucial for success.

The aim of the work is to investigate the revised concept of a neutron detector, offered by Saint Gobain-the BC-704 scintillation screen with a light readout by Wavelength Shifting (WLS) fibers. This detector was developed as a replacement of helium tubes, due to the lack of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He on the world market. It is characterized by high sensitivity to gamma-rays, but the events from neutrons and gammas are well separated. Measurements with gamma and neutron sources have been performed and the results have been compared with helium-3 counter. According to American National Standards Institute (ANSI), we obtained n/γ discrimination on the level of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> , whereas absolute neutron detection efficiency was estimated as approximately two times higher than in the case of the reference <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He tube without the moderator. The tested detector is a sample prototype of one detector configuration of many possible, and that it can be modified to the neutron efficiency specification required.

Several different multiplexing readout methods have been investigated for reading out silicon photomultiplier (SiPM) arrays. However, it is still challenging by using these methods to maintain signal integrity for overall good signal and imaging performance while reducing the number of readout and processing channels. One common issue to resistor based multiplexing method is the position-dependent timing shift among different channels, which can in principle be calibrated and corrected but add complexity to the detector calibration and operation process, and can be very difficult to apply for a practical PET system for routine imaging applications. To solve such and other problems, we explored a capacitor-based multiplexing method for our PET detector to read SiPM with a common cathode which has not been addressed previously. To achieve good detector performance, we required output signal without undershot/overshot suited for excellent charge integration, and without timing shift among different channels. The design applies a capacitor network to divide the charge of signals from a SiPM into two branches, with the division of charge based on the position of the SiPM in the network. Only one capacitor value is needed. The number of readout channels can be reduced from N×N to 2N. Evaluation circuit was tested with pulsed signals and a practical PET detector which consisted of an 8×8 SiPM array and LYSO scintillator array. The results showed that signal rise and fall times from different channels were the similar, no output signal undershot, and no timing shift among different channels. The resistive and capacitive multiplexing methods were compared for their noise level, energy resolution, rise time, and timing resolution as function of channel numbers. Capacitive multiplexing method shows better noise and timing performance with much better timing and energy consistent from all detector area. A PCB circuit board with capacitor multiplexing has been developed for PET detector applications.

In this paper we report on our investigation of the CeBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> timing properties for Time-of-Flight (TOF) Positron Emission Tomography (PET). The TOF detection can significantly improve the signal-to-noise ratio in a reconstructed PET image and reduce the number of events necessary to do the reconstruction. In order to achieve TOF PET, a scintillator must have good timing resolution and good light output. We have investigated seven CeBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> samples of different height, ranging from 3 mm to 37 mm. Two Hamamatsu R4998 fast photomultipliers were used for most experiments. Each sample was measured against a common standard (LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :5%Ce) and the average timing resolution was found to be about 166 ps (fwhm). The two reference (LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :5%Ce) crystals measured against each other gave the timing resolution of 170 ps. The best time resolution of 108 ps (fwhm) was measured for two CeBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> samples (3 and 12 mm height). The longest sample (37 mm) provided 215 ps (fwhm). Two such samples working in coincidence would give about 252 ps timing resolution (fwhm, calculated). We have also measured TOF, where the source was moved between the two detectors and the change in a timing peak position was registered. The results show that a shift of 5 cm could be easily resolved by such a system.

We report on work to develop a system with about 100 picoseconds (ps) time resolution for time of flight positron emission tomography [TOF-PET]. The chosen photo detectors for the study were Silicon Photomultipliers (SiPM's). This study was based on extensive experience in studying timing properties of SiPM's. The readout of these devices used the commercial high speed digitizer DRS4. We applied different algorithms to get the best time resolution of 155 ps Guassian (sigma) for a LYSO crystal coupled to a SiPM. We consider the work as a first step in building a prototype TOF-PET module. The field of positron-emission-tomography (PET) has been rapidly developing. But there are significant limitations in how well current PET scanners can reconstruct images, related to how fast data can be acquired, how much volume they can image, and the spatial and temporal resolution of the generated photons. Typical modern scanners now include multiple rings of detectors, which can image a large volume of the patient. In this type of scanner, one can treat each ring as a separate detector and require coincidences only within the ring, or treat the entire region viewed by the scanner as a single 3 dimensional volume. This 3d technique has significantly better sensitivity since more photon pair trajectories are accepted. However, the scattering of photons within the volume of the patient, and the effect of random coincidences limits the technique. The advent of sub-nanosecond timing resolution detectors means that there is potentially much better rejection of scattered photon events and random coincidence events in the 3D technique. In addition, if the timing is good enough, then the origin of photons pairs can be determined better, resulting in improved spatial resolution - so called 'Time-of-Flight' PET, or TOF-PET. Currently a lot of activity has occurred in applications of SiPMs for TOF-PET. This is due to the devices very good time resolution, low profile, lack of high voltage needed, and their non-sensitivity to magnetic fields. While investigations into this technique have begun elsewhere, we feel that the extensive SiPM characterization and data acquisition expertise of Fermilab, and the historical in-depth research of PET imaging at University of Chicago will combine to make significant strides in this field. We also benefit by a working relationship with the SiPM producer STMicroelectronics (STM).

A fast coincidence preamplifier for solid state radiation detectors

Research on a large-area, cost-effective Muon Telescope Detector has been carried out for RHIC and for next generation detectors at future QCD Lab. We utilize state-of-the-art multi-gap resistive plate chambers with large modules and long readout strips in detector design [1]. The results from cosmic ray and beam test will be presented to address intrinsic timing and spatial resolution for a Long-MRPC. The prototype performance of a novel muon telescope detector at STAR will be reported, including muon identification capability, timing and spatial resolution.